Browsing by Subject "Geoarchaeology."
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Item Age, genesis, and archaeological geology of the sandy mantle on the Gulf Coastal Plain of Texas.(2013-05-15) Ahr, Steven Wayne, 1970-; Nordt, Lee C.; Geology.; Baylor University. Dept. of Geology.Alfisols exhibiting strong textural contrasts between sandy A-E horizons (sandy mantle) and clayey Bt horizons on the Gulf Coastal Plain have invoked debate among pedologists, geologists, and archaeologists about parent material uniformity, the age and origin of the sandy mantle, and the scientific value of buried archaeological sites. This dissertation addresses these issues, as well as climate-related variability in the mass-balance of soil constituents, across a 700-mm mean annual precipitation (MAP) gradient. Five Alfisol pedons located on upland summit settings of the Gulf Coastal Plain of Texas were sampled, described, and analyzed. Depth trends in clay-free particle-size classes and Ti and Zr failed to reveal lithologic discontinuities in each pedon, suggesting that the A-E and Bt horizons are genetically related and the textural contrasts resulted from pedogenic, rather than depositional, processes. Thus, any buried archaeological materials would have moved down the profile under the influence of bioturbation and gravity. Optical dating of the soil profiles illustrates complex age structures. Mixing in the A-E horizons effects apparent OSL ages <10,000 years due to admixture of recently and partially bleached quartz grains. Decreased mixing occurs within Bt horizons, and ages increase systematically with depth. Pedogenic weathering alters 40K, U and Th content and environmental dose rates, with concomitant changes in OSL ages. Apparent maximum age calculations from the probable oldest equivalent dose group in soil parent materials suggest the soils began weathering at least by 90-112 ka, and 40-62 ka, which greatly precedes human entry into North America. Mass-balance trends revealed nearly 100% weathering losses of Ca, Mg, Na, Al, and Fe from the A-E horizons, with redistributions and variable gains in Bt horizons. Elemental flux is positively correlated with net mass flux of fine clay and MAP, likely due to increased weathering-related concentrations of negatively-charged clay particles in higher-MAP soils, which facilitate cation adorption and retention. This has implications for predicting pedogenic response to global climate change and for estimating important soil properties in Alfisol-like paleosols in the geologic record.Item Climatic and human influences on Holocene alluvial history and paleoenvironment of the middle Delaware River Valley, USA.(2012-11-29) Stinchcomb, Gary E.; Driese, Steven G.; Nordt, Lee C.; Geology.; Baylor University. Dept. of Geology.The potential for future prolonged drought episodes in the Northeastern USA is alarming given that a humid climate currently provides water to +50 million people in the northeast, USA. Hydro-climatic projections are hampered by a lack of regionally-based paleoenvironmental reconstructions. The middle Delaware River Valley provides a unique opportunity to expand the Holocene alluvial history and paleoenvironment for the northeast, USA. Thirty-six soil profile descriptions, 332 grain size analyses, and 82 14C ages from trenches and auger borings show that similar alluvial landforms within the river valley have different formation histories and depict a valley that has experienced middle to late Holocene floodplain and terrace reworking. Despite erosion, secular changes in buried soil and sediment properties are closely associated with climate change and land-use. A Holocene time-series was constructed using 149 δ13Csom values from alluvial terrace profiles. There is good agreement between increasing δ13Csom and Panicoideae phytolith concentrations, suggesting that variations in C4 biomass are a contributor to changes in the soil δ13C. A measurement error deconvolution curve over time reveals two isotope stages (II and I), with nine sub-stages exhibiting variations in average δ13Csom (%C4). Stage II, ~10.7-4.3 ka, shows above average δ13Csom (increase %C4) values with evidence of an early Holocene warm/dry interval (sub-stage IIb, 9.8-8.3 ka) that coincides with rapid warming and cool/dry abrupt climate change. Sub-stage IId, 7.0-4.3 ka, is an above average δ13Csom (increase %C4) interval associated with the mid-Holocene warm/dry Hypsithermal. The Stage II-I shift at 4.3 ka documents a transition toward below average δ13Csom (decrease %C4) values, coinciding with decreasing insolation and moisture budget reorganization. Sub-stages Ib and Id (above average %C4) coincide with the first documented occurrence of maize in northeastern USA and population increase during the Late Woodland. These associations suggest that humans influenced δ13Csom during the late Holocene. The influence of land-use is further corroborated by a regionally extensive anthropogenic sedimentation event documented throughout eastern North America, pre-Colonial sediment (PCS) circa: A.D. 1,100–1,600. These data demonstrate that combined prehistoric land-use and climate change impacted eastern North American floodplains several hundred years prior to the onset of European Settlement.Item Geology of the Late Pleistocene artifact-bearing Wasiriya Beds at the Nyamita locality, Rusinga Island, Kenya.(2011-12-19) Van Plantinga, Alexander A.; Peppe, Daniel J.; Geology.; Baylor University. Dept. of Geology.This study investigated the sedimentology and stratigraphy of the Late Pleistocene Wasiriya Beds at the Nyamita locality on Rusinga Island, Kenya in northeastern Lake Victoria. Little is yet known about this region during the Pleistocene. This study provides geological context for archaeological research of the stone artifacts in the Wasiriya Beds, for the paleontological work on the fauna of these beds, and for other paleoenvironmental research in these beds. A robust tephrostratigraphic framework was established using diverse statistical methods. Radiocarbon dates confirm a Late Pleistocene age for these deposits. A valley-drainage model was integrated with a facies model to infer their paleoenvironmental history. Sediments suggest a generally sharply alternating wet and dry seasonality. Geological evidence does not suggest that the Lake Victoria region was especially arid just prior to the Last Glacial Maximum. Additional data from the lower Wasiriya Beds could elaborate on their paleoenvironmental significance.